This invention relates generally to air induction systems and, more specifically, to an air induction system for introducing air into a cavity under a hull of a marine vessel.
The demand for high-speed marine vessels in commercial and military marketplaces continues to build and grow more complex. Driven by a market of fast ferries, offshore petroleum supply vessels, police boats, pleasure craft, and transoceanic vessels and military missions like littoral warfare, patrol craft, and high-speed sealift, a broad variety of vessels has been produced.
Many hull types specialize in certain performance characteristics. Examples are broad-beam hulls like catamarans, and SWATH hull forms, which provide stable platforms. These broad-beam hulls, however, suffer from high power requirements and limited range. Tradeoffs are the norm, and prioritization of vessel performance objectives has resulted in mission-specific optimizations. Passenger vessel technology has reached a plateau in efforts to optimize for speed and fuel efficiency in recent years. The development of wave-piercing hulls, foil assist, and improved waterjet propulsion systems has not overcome drag forces on these submerged hulls, which significantly limit maximum speed, especially in rough seas.
Hydrofoil craft development continues to suffer from a significant xe2x80x9cpower humpxe2x80x9d that results from the combined drag of the displacement hull and foils. Additionally, the relatively narrow beam of these hydrofoil hulls results in low aspect ratio foils and a low foil-borne lift-to-drag ratio. Chosen for their speed and sea-keeping ability, modem hydrofoils are severely limited in range and payload.
The Surface Effect Ship (SES) offers a partial solution to this low-speed dilemma, because an SES operates on a low-drag cushion of air. However, existing SESs expend part of their power levitating the vessel over the water with fans. The remaining SES hull interface with the sea creates a rough and limited operating effectiveness at higher speeds, especially in rough seas. Because of ride and inefficiency, this craft is selected only for its amphibious capabilities.
Thus, in general there is an unmet need in the art to break through hull resistance limitations confronting the technology of high-speed craft. In particular, there is an unmet need in the art for more efficient high-speed hull configurations and structures that can be used, alone and in combination with other technology, such as hydrofoils, so a new performance level can be reached.
The present invention is an air induction system for introducing air under pressure into a cavity under a hull of a marine vessel. The invention converts in a controlled manner kinetic energy of water flowing under a vessel to compress air or gas and releases the air or gas into the cavity to reduce hydrodynamic drag and to maintain an equilibrium pressure to provide buoyancy. Further, the air cavity minimizes marine growth and corrosion on the hull bottom; resulting in reduced maintenance. Thus, the invention provides for more economical operation of marine vessels.
A free stream of flowing water, being relatively dense, has a total pressure greater than desired cavity air pressure at relatively low speeds. The air induction system inducts air, that is draws air, from ambient into a mixing chamber where an air-water mixture attains approximately the same total pressure as the free stream of water. At the end of the mixing chamber the air rises to the surface of the water inside the air cavity at the desired pressure. Excess air suitably escapes at the transom of the vessel. The air induction system parameters may be chosen by the designer to fill the cavity with air in a controlled manner, rather than incidentally entraining into the cavity supplemental air that is drawn from ambient air.
According to the present invention, an air induction system introduces air into a cavity under a hull of a marine vessel. The cavity is bounded by an underside of the hull, first and second sidewalls of the hull, and fore and aft planing surfaces. The air induction system includes an air inlet that is arranged to receive air at ambient pressure. A plenum is arranged to receive air from the air inlet. A fore planing surface has a trailing edge, and the fore planing surface is located toward a bow of the hull. The trailing edge and the plenum define a step having a finite height, and the step extends spanwise substantially a width of the trailing edge. The step is arranged to communicate pneumatically and hydraulically with the plenum. The step generates a first pressure that is less than ambient pressure as the marine vessel moves forwardly through water and a free stream of water moves past the step, such that air communicated from the plenum is entrainable in the free stream of water. A mixing chamber is arranged to communicate pneumatically and hydraulically with the step. The mixing chamber has a predetermined length, and the step and the mixing chamber cooperate to permit kinetic energy of the free stream of water to increase pressure of air entrained in the water as the entrained air moves along the length of the mixing chamber, such that at an aft end of the mixing chamber the entrained air exerts a second pressure that is greater than ambient pressure, and air is exhausted upwardly into the cavity under the hull.
According to another aspect of the invention, an air induction system introduces air into a plurality of cavities or cells under the hull of the marine vessel. Each cell is suitably served by a planing surface terminating in a step, a plenum to receive air or gas and a mixing chamber as previously described. According to the invention, the plurality of cavities increases lateral stability of the marine vessel and automatically trims marine vessels that are unevenlyloaded.